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Max-X High Excursion 15" Subwoofer for only $200 - Build Ideas

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123Toid
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The new Dayton Audio Max-X 15" Subwoofer, the MX15-22 is now available.  I plan to get one, but before I do, I thought I would share some ideas for an enclosure.  As always, the enclosure is the most problematic.  And I honestly thought the MX15-22 would be really hard due to it's High Excursion.  Typically high excursion subwoofers will have some issues with port noise.  Or at least maintaining an inaudible port noise at full volumes.  But if all the specs are correct on this sub, here is a build option.

Home Theater Build

Design

ChevyChev ported design tuned to 21hz in around a 5.3 cubic foot box   Simulation is with 800w

Projected Response:

Response

This Max15-22 has a projected F3 of around 20hz.

Excursion

With 800w, it does have an issue with excursion below 18hz.  Which we can take care of later.

excursion no filter

Port Velocity

Port Velocity below 26hz does go over out target of 17 m/s and has a first port resonance of 226hz.  This is using a slot port of 15" wide by 2" tall and 30" deep.  Some people might be okay with this, as the amount of sound there is negligible.  But I think we can get this down a little more. 

Port Noise no filter

Most of the perceived problems will go away with a simple high pass/subsonic filter on the subwoofer.  By just using a second order centered at 20hz, all your excursion problems go away and your port velocity doesn't go over 17m/s except between 17-25hz.  Here it peaks at 20m/s.  And with a rear firing port, I don't think this would be an issue at all.  But if you were concerned, you could increase that to a 4th order.   Why is this so important?  Most home theater plate amplifiers have a 2nd order high pass on them centered at 20hz.  So you wouldn't have to do anything.

Suggested Amplifiers:

The amplifiers are going to be the most expensive part of this build. There are a lot of pros and cons to each amplifier.  I'll try to break it down for you.

Plate amplifiers

SPA1000 - This would be the most powerful plate amplifier that would get you the most SPL out of the  MC15-22 right out of the box.  It is a class AB amplifier.  The biggest con here is the expense.  It is twice the cost of one subwoofer and will only work for this subwoofer.  But it does have really good dynamic power and will help your subwoofer see it's full potential and has a 20hz 2nd order dedicated high pass.  It also is a sealed amplifier, so you wouldn't have to create a separate amplifier compartment in the box.  However, I still suggest it.

SPA500 - This is another Class ab amplifier, which some people prefer.  This would only give your subwoofer 500w of power and more dynamically.  It also has a very limited parametric EQ, but might help out if you have a huge peak due to a room mode.  This is a cheaper option, but there are less expensive and maybe even better amplifiers out there for the price.  This does have a 20hz 2nd order dedicated high pass as well. It is also sealed, but I would still recommend a separate amplifier compartment. 

SPA500DSP - This is a class D amplifier with built in DSP.  This will allow you to pick your subsonic filter, dsp your room modes out using a laptop with usb. You can install limiters, phasing and eq.  This would be for someone that really wants the best sound out of their subwoofer and has a decent calibrated microphone to set it up.  It is probably my favorite plate amplifier.   This is not enclosed, so I would recommend a separate sealed enclosure for this.  This can be built right into the subwoofer.

SD500 - This is the cheapest option.  It is a class D amplifier.  It has not tested as well as the Dayton Audio AB amplifiers when it comes to dynamic power.  So do not expect much more out of it that the 500w even during short bursts. This is not enclosed, so I would recommend a separate sealed enclosure for this.  This can be built right into the subwoofer.

Professional Amplifiers

Coming Soon

https://www.youtube.com/123toid


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ImCoKeMaN
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Not a lot of constructive feedback on build specifics but this thing better have enough thump that it can be felt not just heard, tune it low, and give it some juice!

Disclaimer: I've been in the forum long enough to know a couple things, but have yet to actually do a speaker build myself =)


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123Toid
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20210416 140937
20210416 140930
20210416 140904
20210416 140856

https://www.youtube.com/123toid


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ElliottDesigns
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Hi Nick,

Do you have a 3D printer? If you do you can create much more optimal ports to reduce turbulence. Or just to optimise port area by creating ports shaped like this:

image

 But always remember guys! 4 separate subs are a lot better for clean bass than 1 big sub. Great bass management video from audioholics here if interested.

I put the link for pt3 because this is the one that talks about putting in positions of 4 subs. Just thought to put this here in case people think of splashing their money on just 1 subwoofer 😉

Elliott Dyson - Mechanical Engineering Student and 3D printing & Design Freelancer


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ElliottDesigns
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I had a thought. Imagine 4 of these beasts in the corners of your room XD

Elliott Dyson - Mechanical Engineering Student and 3D printing & Design Freelancer


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ImCoKeMaN
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@elliottdesigns Yeah, why's it gotta be an or? =)

Disclaimer: I've been in the forum long enough to know a couple things, but have yet to actually do a speaker build myself =)


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Mistersota
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So I was about to get a pair of sql15s when these dropped onto parts express. I decided that the high inductance and steel basket weren't bad enough for me to spend another $120 per sub. I built two 24x20x22" (LxWxH) boxes for them with 1.5x17.5" (with bracing) 42-45' long slot ports. They were originally tuned to 19hz'with ~4 cubic ft volume, but after adding r15 insulation to all the walls (with a thin cloth over it) the tuning was 16-17hz. I still need to finish them, but I'm waiting for a warmer day.

IMG 1401

 The results were just about what I expected. The simulated and response graphs are very close. The only difference is that there is either more inductance than specified, or, more likely, my slot port which has both an extreme aspect ratio and a sharp turn at the back of the box, lost me 2dB. Oh well! I expected that. BTW the response was measured in half space ground plane in my yard. The nearest building was about 100 feet away, but some trees could have contributed to the wavy response above 60hz. I would bring the sub into the field across the street, but its obviously over 100lbs and this is an adequate measurement for my purposes.

I designed these to be EQed and with 6dB of eq and a little taming to the inductance hump. I have a response flat to 16hz with an f3 of 14.6. Honestly, I wasn't expecting to get so much extra volume from the insulation so this is well below what I expected, but the model for 16hz tuning agrees.

responses
mx15 eqed

I don't have a way to measure max spl but my house does certainly shake with both of these running off a crown xls 2502. I'm yet to actually clip the amp because the burst tones were cracking my house and I was worried for my windows.

mx15 max spl

The cone excursion is under xmax at full power down to 14hz. Dayton states a 70%bl of 24mm so I am running a 13hz 4th order high pass. 

mx15 cone excusion

 The port velocity is higher than 17m/s like @123Toid mentioned with his no dsp version, but that only happens around 19hz with a peak of 25.5m/s at 14.5 with the HP filter applied. I heard it when pushing high-power bursts, but it will be inaudible during actual listening.

mx15 port velocity

 Overall, counting wood (2 sheets of 3/4" particle board because MDF prices are crazy high here), subs, minidsp, and amp (Crown 2502 used), I'm almost exactly $1000 into this pair of subs (Excluding the table saw, jigsaw, and router I used). If you get something like a Behringer nx3000 which I've seen for $260 on sweetwater, you could have them for even less. For $1000 there is really nothing else out there that can put out these numbers in cabinets this small. It seems that Dayton has engineered this sub to fit an enclosure that is the perfect size. Small(relative), but not so small that the port won't fit.

I have a friend with dual pb3000s and I don't think they hold up to these, especially at sub 20hz frequencies. Pb4000s seem like a better match. Maybe you guys with more experience with those subs can provide input. If you're looking for performance like that without a few bells and whistles minus $2800, these are great subs for the money.

If you guys are interested in the performance of a sealed version, let me know. I'll need to make a pair for my college apartment when I move back next fall anyway. 


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123Toid
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@mistersota Excellent Build!  Love the idea of lower tuning, my friend and I are doing that on one of his subwoofers, but EQing it down due to cone excursion and port limitations. Looks like you got fantastic results as well.  I am curious what are you using for DSP?  I recently just got the Crown XTI 2002, but I haven't messed with it yet. 

 

I am curious about your cone excursion and your port velocity with this setup.  I really like the setup, but I am not quite getting the same results as you in the simulation.  Did you simulate cone excursion and port velocity with your filters (aka 6dB eq boost and high pass)? When I do this, it looks like the power limitations for cone excursion are closer to 400w.  I might have the wrong information though.  I am simulating a 4 cubic foot box tuned to 16hz using a 6dB boost at 20hz with a 4th order high pass at 14hz. 

 

max x 4 cubic foot

 

https://www.youtube.com/123toid


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Mistersota
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@123toid Under advanced in winisd is an option marked "simulate voice coil inductance". Generally, this isn't important, but with these high excursion subs the voice coils are huge and can have a decent amount. This sub has an inductance of 5.51mH, which is pretty substantial. Fortunately, it isn't that important for a home theater application with dsp. When you simulate it, you'll notice a hump form around 70 hz, a low pass drop above that, and a small loss in low-frequency output. This is likely the problem you are having with xmax. I've included the same simulation, one with inductance and one without. I've also included the values I inputted. I leave a few blank to fill in naturally to see if dayton is stretching their values. The variance shouldn't make a significant difference overall.

mx15 response without inductance
mx15 response inducatance
mx15 parameters

 

As for port velocity, I did show it with the 13hz high pass filter. 

The last and most complicated difference is the cabinet. I try to estimate the theoretical value for cabinet volume caused by the box lining and incorporate it into my design. I find that pink insulation works best. Some people are wary to use it on ported subs because it might spread particles, but I put a thin stretchy material over it to prevent that. 

So originally, my box was 4 cubic feet with a 1.5x17" port which was 45" long. This gets you a box with a tuning of 19hz. This is the response.

mx15 response 4 cubic feet

Then I added the insulation to all the walls, not covering the port in any way, and the port tuning changed to 16.5ish hz. For this to happen, the psuedo box volume had to increase through some sort of fancy science thing I don't fully understand. We know this because we didn't change the port in any way, only the box. To simulate that I entered the tuning I had after the insulation and adjusted the box volume until I had my initial port length. This ended up being 5.5 cubic feet, a 37.5% increase. I was surprised at the large increase in such a big cabinet until I saw that the response was accurate. I then did all my simulations off that value. This is that response.

mx15 response inducatance

When I design cabinets I generally make multiple simulations. One with the true volume, and a couple with larger volumes with the same port length up to 30% larger, sometimes hoping I'll get to that, sometimes just in case. 

I hope this makes sense and I hope my assumptions are right. Through all my builds I have always found them to be true. 

I use a minidsp 2x4 for my dsp. It works fine because my crown has an input sensitivity of .774Vrms or something. It has an output voltage of .9Vrms. I'm not very familiar with the xti amps, but I'm assuming they are similar, but with the DSP built-in? Here's my simulation with the dsp filters I used so you can compare.

mx15 excursion filtered
mx15 resp with filter

 


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123Toid
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@mistersota

Thanks for the explanation.  I appreciate the time and thought put into the design and the further explanation for everyone's benefit.  

I have a few things to consider before building mine.  I love your smaller box, but don't like the longer port.  I was going to try to make it in a way that you wouldn't have to fold it.  I might make it pretty tall and turn it into a stand for my front speakers.

The Crown XTI 2002 does have a DSP built-in.  Not as robust as the mini-dsp. I should mention, that Parts Express was kind enough to give it to me to review on the channel and use to test subwoofers.  I have unboxed it and turned it on, but that is as far as I have gotten with it.  Once I finish the CSS SDX12 build I'll test it out more. But here is a video on the DSP. 

https://www.youtube.com/123toid


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Mistersota
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@123toid yeah the port was really the greatest compromise I made. I've found that having a port that has greater than a 3:1 aspect ratio will begin to lose port output because of resistance caused by the property of <a href=" removed link " target="true">Poiseuille Flow. Sharp 90 degree turns also add resistance. So all around bad in my case lol. 

In your case, passive radiators definitely seem like a good idea, but good enough ones would be expensive and that defeats the purpose of the budget $200 15'' sub. 

Some sort of down-firing port could help eliminate the sound of chuffing allowing you to have a smaller port area. Not sure you'd be able to get it small enough to make a difference though. Good luck with the design! 


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ajc9988
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@mistersota - the port is the only thing on this, but looking at something like this on the MX12-22 (four of them, one in each of a 2.5'-3' 3-way speaker). Here is what I've got:

image
image
image

Now remember, this is a 12" modeled for 2.173ft^3 with a port tuning of 24.53Hz. So not tuned to go as deep as yours, but also a much smaller space than yours. Also, this is not meant to go much above 104 after the DSP is applied to this, the SEAS U18 and the SEAS Titan 27TAC/Gb. So the pop from the inductance should be easily tamed with the DSP in the amp.

How do these sound regarding distortion?


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Mistersota
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@ajc9988 If that's all the SPL you want then the simulation looks pretty good. However, you really are better off going with something like the RSS315HF-4. It has many benefits for your application. 

The mx subs are advertised as max excursion, and their main value is the SPL output they are capable of. In your case, you're not using that. By contrast, the Reference HF line is specifically designed for low distortion, multi-way designs. They have crazy low inductance which would help you more easily cross them with your mid and they also have an aluminum basket. Here is a response without eq comparing it and the mx12 in your cabinet. 

mx12 vs hf12

 As you can see, the inductance is low enough to not bother eqing. The low end is also very similar. If you can squeeze out a little more cabinet volume its performance is even more impressive.

mx12 3 vs hf12

Additionally, since the cabinet volume is larger, you could get a lower tuning with the same length port. This model is tuned to 21hz. With minimal eq (3dB or so) you could get an f3 of 21 hz. A true full-range speaker.

mx12 tuned to 21

 Here are the SPL, excursion, and port velocity graphs. These are assuming a 200 watt signal with dsp applied.

hf12 spl with eq
hf12 excursion with eq
hf12 velocity with eq

I hope this helps. The mx12 would be an adequate driver for your application, but not the best. If the price difference between the drivers isn't too much, the hf12 would be a better fit IMO. 

Since this thread is about the mx drivers, please PM me with any other concerns you might have about the hf12.


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Grumpy
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Drawing1

I worked up a box with using Win ISD. Thoughts?


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Grumpy
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Driver settings
Cone excursion
Max SPL
transfer function magnitude
Port velocity

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